But replacing Megan Fox in the third movie would be like replacing Princess Leia in the Star Wars movies. I mean, they've got an ensemble cast, so why break it up?

Oh well...

But they're not replacing "Leia", they're removing "Jar Jar". Her looks and her acting are all right, but it's her character that went nowhere and simply stops Sam Witwicky from going on adventures in outer space to fight Unicron and save his dumb father from being dropped into Unicron's lava pits while in a dumb robot suit.